Mechanical quantity sensor and  method of manufacturing the same

ABSTRACT

A mechanical quantity sensor includes a first structure having a fixed portion with an opening, a displaceable portion arranged in the opening and displaceable relative to the fixed portion, and a connection portion connecting the fixed portion and the displaceable portion, a second structure having a weight portion joined to the displaceable portion and a pedestal joined to the fixed portion, and arranged and stacked on the first structure, and a base having a driving electrode and a detection electrode arranged on a face facing the weight portion, connected to the pedestal, and arranged and stacked on the second structure. The second structure has a recessed portion arranged in an area on a face of the weight portion facing the second base, the area corresponding to an area where the driving electrode and the detection electrode are not arranged.

TECHNICAL FIELD

The present invention relates to a mechanical quantity sensor detectinga mechanical quantity and a method of manufacturing the same.

BACKGROUND ART

There has been disclosed a technique of an angular velocity sensor,which is structured such that a transducer structure formed of asemiconductor is sandwiched by a pair of glass substrates and joinedthereto, for detecting an angular velocity (see Reference Reference 1:JP-A 2002-350138 (KOKAI)

DISCLOSURE OF THE INVENTION

However, it has been found that when a glass substrate is anodicallybonded to the side of the transducer structure where a movable weight(weight portion) is arranged, it is possible that the weight isattracted to the glass substrate by electrostatic attraction and adheresthereto, and it no longer functions as an angular velocity sensor.Considering this situation, an object of the present invention is toprovide a mechanical quantity sensor and a method of manufacturing thesame, capable of preventing adhesion of the weight (weight portion) tothe glass substrate when the transducer structure formed of asemiconductor and the glass substrate are anodically bonded.

A mechanical quantity sensor according to an aspect of the presentinvention includes: a first structure having a fixed portion with anopening, a displaceable portion arranged in the opening and displaceablerelative to the fixed portion, and a connection portion connecting thefixed portion and the displaceable portion, the first structure beingformed of a first semiconductor material in a plate shape; a secondstructure having a weight portion joined to the displaceable portion anda pedestal arranged surrounding the weight portion and joined to thefixed portion, the second structure being formed of a secondsemiconductor material and arranged and stacked on the first structure;a first base connected to the fixed portion, arranged and stacked on thefirst structure, and formed of an insulating material; and a second basehaving a driving electrode applying vibration in a stacking direction tothe displaceable portion, arranged on a face facing the weight portion,and formed of a conductive material, and a detection electrode detectinga displacement of the displaceable portion, arranged on a face facingthe weight portion, and formed of a conductive material, the second baseformed of an insulating material, connected to the pedestal, andarranged and stacked on the second structure, in which the secondstructure has a recessed portion arranged in an area on a face of theweight portion facing the second base, the area corresponding to an areawhere the driving electrode and the detection electrode are notarranged.

A method of manufacturing a mechanical quantity sensor according to anaspect of the present invention includes: forming a first structurehaving a fixed portion with an opening, a displaceable portion arrangedin the opening and displaceable relative to the fixed portion, and aconnection portion connecting the fixed portion and the displaceableportion, by etching a first layer of a semiconductor substrate formed bysequentially stacking the first layer formed of a first semiconductormaterial, a second layer formed of an insulating material, and a thirdlayer formed of a second semiconductor material; arranging and stackinga first base formed of an insulating material on the first structure byjoining the first base to the fixed portion; by etching the third layer,forming a second structure having a weight portion joined to thedisplaceable portion, a recessed portion arranged on a face of theweight portion on a side opposite to a face joined to the displaceableportion or on a face of an area where the weight portion of the thirdlayer is to be formed on a side opposite to a face joined to thedisplaceable portion, and a pedestal arranged surrounding the weightportion and joined to the fixed portion; and arranging and stacking asecond base on the second structure by anodically bonding the secondbase to the pedestal, the second base formed of an insulating materialand having a first driving electrode arranged on a face facing theweight portion, formed of a conductive material, and applying vibrationin a stacking direction to the displaceable portion, and a firstdetection electrode arranged on a face facing the weight portion, formedof a conductive material, and detecting a displacement of thedisplaceable portion, in which the recessed portion is arranged in anarea corresponding to an area where the first driving electrode and thefirst detection electrode are not arranged.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view showing a state that a mechanicalquantity sensor according to a first embodiment of the present inventionis disassembled.

FIG. 2 is an exploded perspective view showing a state that themechanical quantity sensor in FIG. 1 is disassembled.

FIG. 3 is a top view of a first structure.

FIG. 4 is a top view of a joining part.

FIG. 5 is a top view of a second structure.

FIG. 6 is a bottom view of the second structure.

FIG. 7 is a bottom view of a first base.

FIG. 8 is a top view of a second base.

FIG. 9 is a bottom view of the second base.

FIG. 10 is a cross-sectional view taken along a line B-B in FIG. 1.

FIG. 11 is a cross-sectional view taken along a line C-C in FIG. 1.

FIG. 12 is a cross-sectional view showing six pairs of capacitorelements in the mechanical quantity sensor shown in FIG. 10.

FIG. 13 is a flowchart showing an example of a making procedure of themechanical quantity sensor according to the first embodiment of thepresent invention.

FIG. 14A is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14B is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14C is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14D is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14E is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14F is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14G is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14H is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14I is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14J is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 14K is a cross-sectional view showing a state of the mechanicalquantity sensor in the making procedure in FIG. 13.

FIG. 15 is a view showing a state that a weight portion faces the secondbase when the second base and the second structure are anodicallybonded.

FIG. 16 is an explanatory diagram showing the principle of functioningof a recessed portion as an adhesion preventing part.

FIG. 17 is an exploded perspective view showing a state that amechanical quantity sensor according to a second embodiment of thepresent invention is disassembled.

FIG. 18 is a cross-sectional view taken along a line D-D in FIG. 17.

FIG. 19 is a flowchart showing an example of a making procedure of themechanical quantity sensor according to the second embodiment of thepresent invention.

FIG. 20 is a bottom view of a second structure according to a thirdembodiment.

FIG. 21 is a top view of a second base according to the thirdembodiment.

FIG. 22 is a cross-sectional view showing a mechanical quantity sensoraccording to the third embodiment.

FIG. 23 is a cross-sectional view showing a mechanical quantity sensoraccording to the third embodiment.

EXPLANATION OF CODES

100, 200 . . . mechanical quantity sensor; 110 . . . first structure;111 . . . fixed portion; 111 a . . . frame portion; 111 b, 111 c . . .projecting portion; 112 (112 a-112 e) . . . displaceable portion; 113(113 a-113 d) . . . connection portion; 114 (114 a-114 j) . . . blockupper layer portion; 115 (115 a-115 d) . . . opening; 120, 121, 122, 123. . . joining part; 130 . . . second structure; 131 . . . pedestal; 131a . . . frame portion; 131 b-131 d . . . projecting portion; 132 (132a-133 e) . . . weight portion; 133 . . . opening; 134 (134 a-134 j) . .. block lower layer portion; 135 . . . pocket; 140, 240 . . . firstbase; 141 . . . frame portion; 142 . . . bottom plate portion; 143 . . .recessed portion; 144 a . . . driving electrode; 144 b-144 e . . .detection electrode; 150, 250 . . . second base; 154 a . . . drivingelectrode; 154 b-154 e . . . detection electrode; 160-162, 262 . . .conduction portion; 170 . . . recessed portion; 180 . . . space-chargelayer; 10, 10 a . . . gap; 11 . . . weight-shaped through hole; L1, L2,L4-L11 . . . wiring layer; T1-T11 . . . wiring terminal; E1 . . .driving electrode, detection electrode

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

First Embodiment

FIG. 1 is an exploded perspective view showing a state that a mechanicalquantity sensor 100 is disassembled. The mechanical quantity sensor 100has a first structure 110, a joining part 120, and a second structure130 which are stacked one another, and a first base 140 and a secondbase 150.

FIG. 2 is an exploded perspective view showing a state that part (firststructure 110 and second structure 130) of the mechanical quantitysensor 100 is further disassembled. FIG. 3, FIG. 4, FIG. 5, and FIG. 6are a top view of the first structure 110, a top view of the joiningpart 120, a top view of the second structure 130, and a bottom view ofthe second structure, respectively. FIG. 7, FIG. 8, and FIG. 9 are abottom view of the first base 140, a top view of the second base 150,and a bottom view of the second base 150, respectively. FIG. 10 and FIG.11 are cross-sectional views of the mechanical quantity sensor 100 takenalong a line B-B and a line C-C of FIG. 1.

The mechanical quantity sensor 100 functions by itself or in combinationwith a circuit board (for example, mounted on a board) as an electroniccomponent. The mechanical quantity sensor 100 as an electronic componentcan be mounted in a game machine, a mobile terminal (for example, acellular phone), or the like. In addition, the mechanical quantitysensor 100 and the circuit board (active elements such as IC and wiringterminals on the circuit board) are connected electrically by wirebonding, flip-chip bonding, or the like.

The mechanical quantity sensor 100 is capable of measuring one or bothof an acceleration α and an angular velocity ω. That is, a mechanicalquantity means one or both of the acceleration a and the angularvelocity ω. Accelerations αx, αy, αz can be measured by detectingdisplacements of a displaceable portion 112 (which will be describedlater) caused by forces F0 x, F0 y, F0 z in X, Y, Z-axis directions,respectively. Further, angular velocities ωx, ωy in X, Y-axis directionsrespectively can be measured by vibrating the displaceable portion 112in the Z-axis direction and detecting displacements of the displaceableportion 112 caused by Coriolis forces Fy, Fx in Y, X-axis directions,respectively. In this manner, the mechanical quantity sensor 100 iscapable of measuring the accelerations αx, αy, αz in three axes and theangular velocities ωx, ωy in two axes. Note that details of this will bedescribed later.

The first structure 110, the joining part 120, the second structure 130,the first base 140, and the second base 150 each have a substantiallysquare outer periphery with each side being 5 mm for example, and haveheights of, for example, 20 μm, 2 μm, 675 μm, 500 μm, and 500 μm,respectively.

The first structure 110, the joining part 120, and the second structure130 can be formed of silicon, silicon oxide, and silicon, respectively,and the mechanical quantity sensor 100 can be manufactured using an SOI(Silicon On Insulator) substrate forming a three-layer structure ofsilicon/silicon oxide/silicon. For the silicon forming the firststructure 110 and the second structure 130, it is preferable to use aconductive material containing impurities, for example boron or thelike, in its entirety. As will be described later, use of siliconcontaining impurities for forming the first structure 110 and the secondstructure 130 allows to simplify wiring of the mechanical quantitysensor 100. In this embodiment, silicon containing impurities is usedfor the first structure 110 and the second structure 130.

Further, the first base 140 and the second base 150 can each be formedof a glass material.

The first structure 110 has a substantially square outer shape, and ismade up of a fixed portion 111 (111 a to 111 c), a displaceable portion112 (112 a to 112 e), a connection portion 113 (113 a to 113 d), and ablock upper layer portion 114 (114 a to 114 j). The first structure 110can be made by etching a film of a semiconductor material and formingopenings 114 a to 114 d and block upper layer portions 114 a to 114 j.

The fixed portion 111 can be separated into a frame portion 111 a andprojecting portions 111 b, 111 c. The frame portion 111 a is aframe-shaped substrate with an outer periphery and an inner peripheryboth being a substantially square. The projecting portion 111 b is asubstantially square substrate, arranged at a corner portion on theinner periphery of the frame portion 111 a and projecting toward thedisplaceable portion 112 b (in a 0° direction when an X direction of theX-Y plane is 0°). The projecting portion 111 c is a substantially squaresubstrate, arranged at a corner portion on the inner periphery of theframe portion 111 a and projecting toward the displaceable portion 112 d(in a 180° direction when an X direction of the X-Y plane is 0°). Theframe portion 111 a and the projecting portions 111 b, 111 c are formedintegrally.

The displaceable portion 112 is made up of displaceable portions 112 ato 112 e. The displaceable portion 112 a is a substrate having asubstantially square outer periphery and is arranged in the vicinity ofthe center of an opening of the fixed portion 111. The displaceableportions 112 b to 112 e are substrates each having a substantiallysquare outer periphery and are connected and arranged so as to surroundthe displaceable portion 112 a from four directions (X-axis positivedirection, X-axis negative direction, Y-axis positive direction, andY-axis negative direction). The displaceable portions 112 a to 112 e arejoined respectively to weight portions 132 a to 132 e which will bedescribed later by the joining part 120, and are displaced integrallyrelative to the fixed portion 111.

An upper face of the displaceable portion 112 a functions as a drivingelectrode E1 (which will be described later). The driving electrode E1on the upper face of the displaceable portion 112 a capacitively couplesto a driving electrode 144 a, which will be described later, disposed ona lower face of the first base 140, and the displaceable portion 112 isvibrated in the Z-axis direction by voltage applied therebetween. Notethat details of this driving will be described later.

Upper faces of the displaceable portions 112 b to 112 e each function asa detection electrode E1 (which will be described later) detectingdisplacements in the X-axis and Y-axis directions of the displaceableportion 112. The detection electrodes on the upper faces of thedisplaceable portions 112 b to 112 e capacitively couple respectively todetection electrodes 144 b to 144 e, which will be described later,disposed on a lower face of the first base 140 (the alphabets b to e ofthe displaceable portions 112 correspond to the alphabets b to e of thedetection electrodes 144 in order respectively). Note that details ofthis detection will be described later.

The connection portions 113 a to 113 d are substantially rectangularsubstrates connecting the fixed portion 111 and the displaceable portion112 a in four directions (45°, 135°, 225°, 315° directions when the Xdirection of the X-Y plane is 0°).

Areas of the connection portions 113 a to 113 d close to the frameportion 111 a are joined by the joining part 120 to projecting portions131 c of a pedestal 131 (which will be described later). For other areasof the connection portions 113 a to 113 d, that is, areas close to thedisplaceable portion 112 a, the projecting portions 131 c are not formedin the corresponding areas, and these areas have a small thickness andhence have flexibility. The reason that the areas of the connectionportions 113 a to 113 d close to the frame portion 111 a are joined tothe projecting portions 131 c is to prevent damage to the connectionportions 113 a to 113 d by large deflection.

The connection portions 113 a to 113 d function as deflectable beams.Deflection of the connection portions 113 a to 113 d can displace thedisplaceable portion 112 relative to the fixed portion 111.Specifically, the displaceable portion 112 is displaced linearly in a Zpositive direction and a Z negative direction relative to the fixedportion 111. Further, the displaceable portion 112 is capable ofrotating positively or negatively with the X-axis and Y-axis beingrotation axes, relative to the fixed portion 111. That is, the“displacement” mentioned here can include both movement and rotation(movement in the Z-axis direction and rotation about the X, Y axes).

The block upper layer portion 114 is made up of block upper layerportions 114 a to 114 j. The block upper layer portions 114 a to 114 jare substantially square substrates and are arranged along the innerperiphery of the fixed portion 111 so as to surround the displaceableportion 112 from its periphery.

The block upper layer portions 114 h, 114 a have end faces facing endfaces of the displaceable portion 112 e, and the block upper layerportions 114 b, 114 c have end faces facing end faces of thedisplaceable portion 112 b. The block upper layer portions 114 d, 114 ehave end faces facing end faces of the displaceable portion 112 c, andthe block upper layer portions 114 f, 114 g have end faces facing endfaces of the displaceable portion 112 d. As shown in FIG. 1, the blockupper layer portions 114 a to 114 h each have the end face facing one ofeight end faces of the displaceable portion 112, and are arrangedclockwise in alphabetical order. The block upper layer portion 114 i andthe block upper layer portion 114 j are arranged in 90°, 270° directionswhen the X direction of the X-Y plane is 0°.

The block upper layer portions 114 a to 114 h are joined respectively toblock lower layer portions 134 a to 134 h, which will be describedlater, by the joining part 120 (the alphabets a to h of the block upperlayer portions 114 correspond to the alphabets a to h of the block lowerlayer portions 134 in order respectively). The blocks made by joiningthe block upper layer portions 114 a to 114 h and the block lower layerportions 134 a to 134 h, respectively, are used for the purpose ofwiring for supplying power to detection electrodes 144 b to 144 e, 154 bto 154 e, which will be described later.

The block upper layer portions 114 i, 114 j are joined respectively toblock lower layer portions 134 i, 134 j, which will be described later,by the joining part 120. The block made by joining the block upper layerportions 114 i, 114 j and the block lower layer portions 134 i, 134 j,respectively, are used for the purpose of wiring for vibrating thedisplaceable portion 112 in the Z-axis direction. Note that details ofthis will be described later.

The second structure 130 has a substantially square outer shape, and ismade up of a pedestal 131 (131 a to 131 d), a weight portion 132 (132 ato 132 e), and a block lower layer portion 134 (134 a to 134 j). Thesecond structure 130 can be made by etching a substrate of asemiconductor material to form an opening 133, block lower layerportions 134 a to 134 j, and a pocket 135 (which will be describedlater). In addition, the pedestal 131 and the block lower layer portions134 a to 134 j are substantially equal in height, and the weight portion132 is lower in height than the pedestal 131 and the block lower layerportions 134 a to 134 j. This is for securing a space (gap) between theweight portion 132 and the second base 150 for allowing the weightportion 132 to be displaced. The pedestal 131, the block lower layerportions 134 a to 134 j, and the weight portion 132 are arrangedseparately from each other.

The pedestal 131 can be separated into a frame portion 131 a andprojecting portions 131 b to 131 d.

The frame portion 131 a is a frame-shaped substrate with an outerperiphery and an inner periphery both being a substantially square, andhas a shape corresponding to the frame portion 111 a of the fixedportion 111.

The projecting portion 131 b is a substantially square substrate,arranged at a corner portion on the inner periphery of the frame portion131 a and projecting toward the weight portion 132 b (in a 0° directionwhen the X direction of the X-Y plane is 0°), and has a shapecorresponding to the projecting portion 111 b of the fixed portion 111.

The projecting portions 131 c are four substantially rectangularsubstrates, projecting toward the weight portion 132 a from the frameportion 131 a in 45°, 135°, 225°, 315° directions respectively when theX direction of the X-Y plane is 0°, and having one ends connected to theframe portion 131 a of the pedestal 131 and the other ends arrangedseparately from the weight portion 132 a. The projecting portions 131 care formed in substantially half areas on the frame portion 131 a sidein the areas corresponding to the connection portions 113 a to 113 d,and are not formed in other areas, that is, substantially half areas onthe weight portion 132 side.

The projecting portion 131 d is a substantially square substrate,arranged at a corner portion on the inner periphery of the frame portion131 a and projecting toward the weight portion 132 d (in the 180°direction when X direction of the X-Y plane is 0°), in which a pocket135 (opening) penetrating through a front face and a rear face of thissubstrate is formed, and is joined to the projecting portion 111 c ofthe fixed portion 111.

The pocket 135 is a rectangular parallelepiped space for example, inwhich a getter material for maintaining a high vacuum is placed. Oneopening end of the pocket 135 is covered by the joining part 120. Mostpart of the other opening end of the pocket 135 is covered by the secondbase 150, but a part thereof near the weight portion 132 is not covered.This other opening end and the opening 133 in which the weight portion132 and so on are formed communicate partly with each other (not shown).

The getter material absorbs a residue gas for the purpose of increasingthe degree of vacuum in the mechanical quantity sensor 100 which isvacuum sealed. This allows to reduce the effect of air resistance whenthe displaceable portion 112 (and the weight portion 132) vibrates. Asthe getter material used for the mechanical quantity sensor 100, forexample, a mixture of titanium and a Zr—V—Fe alloy (made by SAES GettersJapan, product name: Non-evaporable Getter St122) can be used.

The frame portion 131 a and the projecting portions 131 b to 131 d areformed integrally.

The pedestal 131 is connected to the fixed portion 111 and predeterminedareas of the connection portions 113 a to 113 d by the joining part 120.

The weight portion 132 functions as a heavy weight or an operating bodyhaving amass and receiving the force F0 and the Coriolis force F causedby the acceleration α and the angular velocity ω respectively. That is,when the acceleration α and the angular velocity ω are applied, theforce F0 and the Coriolis force F act on the center of gravity of theweight portion 132.

The weight portion 132 is separated into weight portions 132 a to 132 ehaving a rectangular parallelepiped shape. The weight portions 132 b to132 e are connected from four directions to the weight portion 132 aarranged in the center, and are displaceable (movable, rotatable)integrally as a whole. That is, the weight portion 132 a functions as aconnection portion connecting the weight portions 132 b to 132 e.

The weight portions 132 a to 132 e have substantially squarecross-sectional shapes corresponding to the displaceable portions 112 ato 112 e, respectively, and are joined to the displaceable portions 112a to 112 e by the joining part 120. The displaceable portion 112 isdisplaced according to the force F0 and the Coriolis force F applied tothe weight portion 132, and consequently, it becomes possible to measurethe acceleration α and the angular velocity ω.

The reason that the weight portion 132 is made up of the weight portions132 a to 132 e is to achieve both reduction in size and increase insensitivity of the mechanical quantity sensor 100. When the mechanicalquantity sensor 100 is reduced in size (reduced in capacity), thecapacity of the weight portion 132 decreases, and its mass decreases,resulting in decreased sensitivity to the mechanical quantity. Dispersedarrangement of the weight portions 132 b to 132 e which does not hinderdeflections of the connection portions 113 a to 113 d assures the massof the weight portions 132. Consequently, the reduction in size and theincrease in sensitivity of the mechanical quantity sensor 100 are bothachieved.

A rear face of the weight portion 132 a functions as a driving electrodeE1 (which will be described later). This driving electrode E1 on therear face of the weight portion 132 a capacitively couples to a drivingelectrode 154 a, which will be described later, disposed on an upperface of the second base 150, and the displaceable portion 112 isvibrated in the Z-axis direction by voltage applied therebetween. Notethat details of this driving will be described later.

Rear faces of the weight portions 132 b to 132 e each function as adetection electrode E1 (which will be described later) detecting adisplacement of the displaceable portion 112 in the X-axis and Y-axisdirections. The detection electrodes E1 on the rear faces of the weightportions 132 b to 132 e capacitively couple respectively to detectionelectrodes 154 b to 154 e, which will be described later, disposed onthe upper face of the second base 150 (the alphabets b to e of theweight portion 132 correspond to the alphabets b to e of the detectionelectrodes 154 in order respectively). Note that details of thisdetection will be described later.

Recessed portions 170 are arranged in the areas corresponding to areason the rear face of the weight portion 132 where the driving electrode154 a and the detection electrodes 154 b to 154 e, which will bedescribed later, are not arranged. This arrangement is for preventing,when the second base 150 and the second structure 130 are anodicallybonded, the weight portion 132 from being pressed onto the drivingelectrode 154 a and the detection electrodes 154 b to 154 e byelectrostatic attraction, sinking into them and adhering thereto.

As shown in FIG. 6, in this embodiment, there are provided four recessedportions 170 in total on the rear face of the weight portion 132 a, oneby one in the areas corresponding to spaces between the drivingelectrode 154 a and the detection electrodes 154 b to 154 e,respectively.

Conventionally, when the second base 150 and the second structure 130are anodically bonded (when the second glass substrate is anodicallybonded), it is possible that the weight portion 132 is attracted andjoined to the second base 150 by electrostatic attraction and adheringthereto, and the weight portion 132 does not operate, resulting in astate of not functioning as the mechanical quantity sensor 100.

Providing the recessed portions 170 allows to reduce electrostaticattraction between the weight portion 132 and the second base 150 whenthe second base 150 and the second structure 130 are anodically bonded.Note that details of this will be described later.

Sides 171, 172 of each recessed portion 170 are arranged at positionscorresponding to outer peripheries of the driving electrode 154 a andthe detection electrodes 154 b to 154 e. As a result, the recessedportions 170 each have an L-shaped outline. In this embodiment, the fourrecessed portions 170 are separated from each other, but it is alsopossible that the four recessed portions 170 have shapes coupled to eachother.

The depth of the recessed portions 170 can be, for example, 5 μm so thatthey adequately function as adhesion preventing parts.

Here, an area on the rear face of the weight portion 132 causingelectrostatic attraction to the second base 150 is an area A0 which doesnot correspond to the driving electrode 154 a and the detectionelectrodes 154 b to 154 e on the rear face of the weight portion 132 a.In this embodiment, the recessed portions 170 are formed in the entirearea A0. That is, this area A0 matches the areas where the recessedportions 170 are formed. However, it is not always necessary to form therecessed portions 170 in the entire area A0.

The block lower layer portions 134 a to 134 j have substantially squarecross-sectional shapes corresponding to those of the block upper layerportions 114 a to 114 j, respectively, and are joined to the block upperlayer portions 114 a to 114 j by the joining part 120. Blocks made byjoining the block upper layer portions 114 a to 114 h and the blocklower layer portions 134 a to 134 h are hereinafter referred to as“blocks a to h”, respectively.

The blocks a to h are used for the purpose of wirings to supply power todetection electrodes 144 b to 144 e, 154 b to 154 e, respectively.Blocks made by joining the block upper layer portions 114 i, 114 j andthe block lower layer portions 134 i, 134 j, respectively (hereinafterreferred to as “blocks i, j” respectively), are used for the purpose ofwirings for vibrating the displaceable portion 112 in the Z-axisdirection. Note that details of this will be described later.

The joining part 120 connects the first, second structures 110, 130 asalready described. The joining part 120 is separated into a joining part121 connecting the predetermined areas of the connection portions 113and the fixed portion 111 to the pedestal 131, a joining part 122 (122 ato 122 e) connecting the displaceable portions 112 a to 112 e to theweight portions 132 a to 133 e, and a joining part 123 (123 a to 123 j)connecting the block upper layer portions 114 a to 114 j to the blocklower layer portions 134 a to 134 j. Other than these portions, thejoining part 120 does not connect the first and second structures 110,130. This is for allowing the connection portions 113 a to 113 d todeflect and the weight portion 132 to be displaced.

In addition, the joining parts 121, 122, 123 can be formed by etching asilicon oxide film.

Conduction portions 160 to 162 are formed for establishing conduction ofthe first structure 110 and the second structure 130 at necessaryportions.

The conduction portion 160 establishes conduction between the fixedportion 111 and the pedestal 131, and penetrates the projecting portion111 b of the fixed portion 111 and the joining part 121.

The conduction portion 161 establishes conduction between thedisplaceable portion 112 and the weight portion 132, and penetrates thedisplaceable portion 112 a and the joining part 122.

The conduction portions 162 establish conduction between the block upperlayer portions 114 a, 114 b, 114 e, 114 f, 114 i and the block lowerlayer portions 134 a, 134 b, 134 e, 134 f, 134 i respectively, andpenetrate the block upper layer portions 114 a, 114 b, 114 e, 114 f, 114i and the joining part 123 respectively.

The conduction portions 160 to 162 are made by forming, for example,metal layers of Al or the like on, for example, edges, wall faces andbottom portions of through holes. In addition, although shapes of thethrough holes are not particularly limited, the through holes of theconduction portions 160 to 162 are preferred to be formed in truncatedconical shapes because they allow to form metal layers effectively bysputtering or the like of Al or the like.

The first base 140 is formed of, for example, a glass material, has asubstantially parallelepiped outer shape, and has a frame portion 141and a bottom plate portion 142. The frame portion 141 and the bottomplate portion 142 can be made by forming a recessed portion 143 in asubstantially rectangular parallelepiped shape (for example, 2.5 mmsquare and 5 μm deep) in a substrate.

The frame portion 141 has a substrate shape that is a frame shape withan outer periphery and an inner periphery both being a substantiallysquare. The outer periphery of the frame portion 141 matches the outerperiphery of the fixed portion 111, and the inner periphery of the frameportion 141 is smaller than the inner periphery of the fixed portion111.

The bottom plate portion 142 has a substantially square substrate shapehaving an outer periphery that is substantially the same as that of theframe portion 141.

The reason that the recessed portion 143 is formed in the first base 140is to secure a space for allowing the displaceable portion 112 to bedisplaced. The first structure 110 excluding the displaceable portion112, that is, the fixed portion 111 and the block upper layer portions114 a to 114 j are joined to the first base 140 by anodic bonding forexample.

On the bottom plate portion 142 (on a rear face of the first base 140),a driving electrode 144 a and detection electrodes 144 b to 144 e arearranged so as to face the displaceable portion 112. The drivingelectrode 144 a and the detection electrodes 144 b to 144 e can all beformed of a conductive material. The driving electrode 144 a is crossshaped for example and is formed in the vicinity of the center of therecessed portion 143 so as to face the displaceable portion 112 a. Thedetection electrodes 144 b to 144 e each have a substantially squareshape, surrounding the driving electrode 144 a from four directions (theX-axis positive direction, the X-axis negative direction, the Y-axispositive direction, and the Y-axis negative direction), and are arrangedto face the displaceable portions 112 b to 112 e in order respectively.The driving electrode 144 a and the detection electrodes 144 b to 144 eare separated from each other.

A wiring layer L1 electrically connected to an upper face of the blockupper layer portion 114 i is connected to the driving electrode 144 a. Awiring layer L4 electrically connected to an upper face of the blockupper layer portion 114 b is connected to the detection electrode 144 b.A wiring layer L5 electrically connected to an upper face of the blockupper layer portion 114 e is connected to the detection electrode 144 c.A wiring layer L6 electrically connected to an upper face of the blockupper layer portion 114 f is connected to the detection electrode 144 d.A wiring layer L7 electrically connected to an upper face of the blockupper layer portion 114 a is connected to the detection electrode 144 e.

As a constituent material for the driving electrode 144 a, the detectionelectrodes 144 b to 144 e, and the wiring layers L1, L4 to L7, Alcontaining Nd can be used for example.

Use of the Al containing Nd for the driving electrode 144 a, thedetection electrodes 144 b to 144 e, and the like allows to suppressformation of hillocks on the driving electrode 144 a, the detectionelectrodes 144 b to 144 e, and the like during a heat treatment process(anodic bonding of the first base 140 or the second base 150 andactivation of the getter material) which will be described later. Thehillocks mentioned here are, for example, hemispheric projections. Thus,dimensional accuracy can be increased for a distance between the drivingelectrode 144 a and the driving electrode E1 (which capacitively couplesto the driving electrode 144 a) formed on the upper face of thedisplaceable portion 112 a and distances between the detectionelectrodes 144 b to 144 e and the detection electrodes E1 (whichcapacitively couple to the detection electrodes 144 b to 144 e in order,respectively) formed on the upper faces of the displaceable portions 112b to 112 e, respectively. Since the dimensional accuracy between thedriving electrodes 144 a, E1 and between the detection electrodes 144 bto 144 e, E1 can thus be increased, consequently dispersion ofelectrostatic capacitance values can be reduced, and dispersion ofcharacteristics among products can be suppressed.

The second base 150 is made of a glass material for example, and has asubstantially square substrate shape. The second structure 130 excludingthe weight portion 132, that is, the pedestal 131 and the block lowerlayer portions 134 a to 134 j are joined to the second base 150 byanodic bonding for example. The weight portion 132 is lower in heightthan the pedestal 131 and the block lower layer portions 134 a to 134 j,and thus is not joined to the second base 150. This is for securing aspace (gap) between the weight portion 132 and the second base 150 forallowing the weight portion 132 to be displaced.

On the upper face of the second base 150, a driving electrode 154 a anddetection electrodes 154 b to 154 e are arranged so as to face theweight portion 132. The driving electrode 154 a and the detectionelectrodes 154 b to 154 e can all be formed of a conductive material.The driving electrode 154 a is cross shaped for example and is formed inthe vicinity of the center of the upper face of the second base 150 soas to face the weight portion 132 a. The detection electrodes 154 b to154 e each have a substantially square shape, surrounding the drivingelectrode 154 a from four directions (the X-axis positive direction, theX-axis negative direction, the Y-axis positive direction, and the Y-axisnegative direction), and are arranged to face the weight portions 132 bto 132 e in order respectively. The driving electrode 154 a and thedetection electrodes 154 b to 154 e are separated from each other.

A wiring layer L2 electrically connected to a rear face of the blocklower layer portion 134 j is connected to the driving electrode 154 a.

A wiring layer L8 electrically connected to a rear face of the blocklower layer portion 134 c is connected to the detection electrode 154 b.A wiring layer L9 electrically connected to a rear face of the blocklower layer portion 134 d is connected to the detection electrode 154 c.A wiring layer L10 electrically connected to a rear face of the blocklower layer portion 134 g is connected to the detection electrode 154 d.A wiring layer L11 electrically connected to a rear face of the blocklower layer portion 134 h is connected to the detection electrode 154 e.

As a constituent material for the driving electrode 154 a, the detectionelectrodes 154 b to 154 e, and the wiring layers L2, L8 to L11, Alcontaining Nd can be used for example.

Use of the Al containing Nd for the driving electrode 154 a and thedetection electrodes 154 b to 154 e allows to suppress formation ofhillocks on the driving electrode 154 a, the detection electrodes 154 bto 154 e, and the like during a heat treatment process (anodic bondingof the second base 150 and activation of the getter material) which willbe described later. Thus, dimensional accuracy can be increased for adistance between the driving electrode 154 a and the driving electrodeE1 (which capacitively couples to the driving electrode 154 a) formed ona lower face of the weight portion 132 a and distances between thedetection electrodes 154 b to 154 e and the detection electrodes E1(which capacitively couple to the detection electrodes 154 b to 154 e inorder, respectively) formed on the upper faces of the weight portions132 b to 132 e, respectively. Since the dimensional accuracy between thedriving electrodes 154 a, E1 and between the detection electrodes 154 bto 154 e, E1 can thus be increased, consequently dispersion ofelectrostatic capacitance values can be reduced, and dispersion ofcharacteristics among products can be suppressed.

Wiring terminals T (T1 to T11) penetrating the second base 150 areprovided in the second base 150, which allow electrical connection fromthe outside of the mechanical quantity sensor 100 to the drivingelectrodes 144 a, 154 a, the detection electrodes 144 b to 144 e, 154 bto 154 e.

An upper end of the wiring terminal T1 is connected to a rear face ofthe projecting portion 131 b of the pedestal 131. The wiring terminalsT2 to T9 are connected to the rear faces of the block lower layerportions 134 a to 134 h, respectively (the numerical order of T2 to T9of the wiring terminals T2 to T9 corresponds to the alphabetical orderof 134 a to 134 h of the block lower layer portions 134 a to 134 h,respectively). The wiring terminals T10, T11 are connected to the rearfaces of the block lower layer portions 134 i, 134 j, respectively.

As shown in FIG. 10 and FIG. 11, the wiring terminals T are made byforming, for example, metal films of Al or the like on, for example,edges, wall faces and bottom portions of truncated conical throughholes, and has structures similar to the conduction portions 160 to 162.The wiring terminals T can be used as connection terminals forconnection to an external circuit by wire bonding for example.

Note that in FIG. 1 to FIG. 11, the second base 150 is illustrated to bearranged on a lower side for making it easy to see the first structure110, the joining part 120, and the second structure 130. When the wiringterminals T and an external circuit are connected by wire bonding forexample, the second base 150 of the mechanical quantity sensor 100 canbe arranged on an upper side for example, so as to facilitate theconnection.

(Operation and Wiring of the Mechanical Quantity Sensor 100)

The wiring and electrodes of the mechanical quantity sensor 100 will bedescribed.

FIG. 12 is a cross-sectional view showing six pairs of capacitorelements in the mechanical quantity sensor 100 shown in FIG. 10. FIG. 11shows a portion to function as an electrode by hatching. Note thatalthough the six pairs of capacitor elements are shown in FIG. 11, tenpairs of capacitor elements are formed in the mechanical quantity sensor100 as described above.

One electrodes of the ten pairs of capacitor elements are the drivingelectrode 144 a and the detection electrodes 144 b to 144 e formed onthe first base 140, and the driving electrode 154 a and the detectionelectrodes 154 b to 154 e formed on the second base 150.

The other electrodes of the ten pairs of capacitor elements are thedriving electrode E1 on the upper face of the displaceable portion 112 aand the detection electrodes E1 formed respectively on the upper facesof the displaceable portions 112 b to 112 e, the driving electrode E1 ona lower face of the weight portion 132 a, and the detection electrodesE1 formed on lower faces of the weight portions 132 b to 132 e,respectively. That is, a block made by joining the displaceable portion112 and the weight portion 132 functions as a common electrode for tenpairs of capacitive couplings. Since the first structure 110 and thesecond structure 130 are formed of the conductive material (siliconcontaining impurities), the block made by joining the displaceableportion 112 and the weight portion 132 can function as an electrode.

The capacitance of a capacitor is in inverse proportion to the distancebetween electrodes, and thus it is assumed that the driving electrodesE1 and the detection electrodes E1 are present on an upper face of thedisplaceable portion 112 and a lower face of the weight portion 132.That is, the driving electrodes E1 and the detection electrodes E1 arenot formed as separate bodies on outer layers of the upper face of thedisplaceable portion 112 and the lower face of the weight portion 132.It is understood that the upper face of the displaceable portion 112 andthe lower face of the weight portion 132 function as the drivingelectrodes E1 and the detection electrodes E1.

The driving electrode 144 a and the detection electrodes 144 b to 144 eformed on the first base 140 are electrically connected to the blockupper layer portions 114 i, 114 b, 114 e, 114 f, 114 a via the wiringlayers L1, L4 to L7 in order respectively. Further, conduction betweenthe block upper layer portions 114 i, 114 b, 114 e, 114 f, 114 a and theblock lower layer portions 134 i, 134 b, 134 e, 134 f, 134 arespectively is established by the conduction portion 162.

The driving electrode 154 a and the detection electrodes 154 b to 154 eformed in the second base 150 are electrically connected to the blocklower layer portions 134 j, 134 c, 134 d, 134 g, 134 h via the wiringlayers L2, L8 to L11 in order respectively.

Therefore, wirings to these driving electrodes 144 a, 154 a anddetection electrodes 144 b to 144 e, 154 b to 154 e just need to beconnected to lower faces of the block lower layer portions 134 a to 134j. The wiring terminals T2 to T9 are arranged on the lower faces of theblock lower layer portions 134 a to 134 h respectively, and the wiringterminals T10, T11 are arranged on the lower faces of the block lowerlayer portions 134 i, 134 j respectively.

Accordingly, the wiring terminals T2 to T11 are electrically connectedto the detection electrodes 144 e, 144 b, 154 b, 154 c, 144 c, 144 d,154 d, 154 e and the driving electrodes 144 a, 154 a in orderrespectively.

The driving electrodes E1 and the detection electrodes E1 are formed bythe upper face of the displaceable portion 112 and the lower face of theweight portion 132, respectively. Conduction between the displaceableportion 112 and the weight portion 132 is established by the conductionportion 161, and they are both formed of a conductive material.Conduction between the pedestal 131 and the fixed portion 111 isestablished by the conduction portion 160, and they are both formed of aconductive material. The displaceable portion 112, the connectionportion 113, and the fixed portion 111 are formed integrally of aconductive material. Therefore, wirings to the driving electrodes E1 andthe detection electrodes E1 just need to be connected to a lower face ofthe pedestal 131. The wiring terminal T1 is arranged on a lower face ofthe projecting portion 131 b of the pedestal 131, and the wiringterminal T1 is electrically connected to the driving electrodes E1 andthe detection electrodes E1.

As described above, since the first structure 110 and the secondstructure 130 are formed of the conductive material (silicon containingimpurities), the blocks a to j made by joining the block upper layerportions 114 a to 114 j and the block lower layer portions 134 a to 134j can have a function as a wiring, and thus the wirings to the capacitorelements can be simplified.

The principle of detection of the acceleration and the angular velocityby the mechanical quantity sensor 100 will be described.

(1) Vibration of Displaceable Portion 112

When voltage is applied between the driving electrodes 144 a, E1, thedriving electrodes 144 a, E1 attract each other by Coulomb force, andthe displaceable portion 112 (and the weight portion 132) is displacedin the Z-axis positive direction. Further, when voltage is appliedbetween the driving electrodes 154 a, E1, the driving electrodes 154 a,E1 attract each other by Coulomb force, and the displaceable portion 112(and the weight portion 132) is displaced in the Z-axis negativedirection. That is, by applying voltage between the driving electrodes144 a, E1 and between the driving electrodes 154 a, E1 alternately, thedisplaceable portion 112 (and the weight portion 132) vibrates in theZ-axis direction. For this application of voltage, a positive ornegative direct-current waveform (or pulsed waveform whennon-application time is considered), a half-wave waveform, or the likecan be used.

In addition, the driving electrodes 144 a, E1 (the upper face of thedisplaceable portion 112 a) and the driving electrodes 154 a, E1 (thelower face of the weight portion 132 a) function as a vibration applier,and the detection electrodes 144 b to 144 e, 154 b to 154 e, and E1 (theupper faces of the displaceable portions 112 b to 112 e, and the lowerfaces of the weight portions 132 b to 132 e) function as a displacementdetector.

The cycle of vibration of the displaceable portion 112 is determined bya switching cycle of voltage. It is preferable that this cycle ofswitching is close to the natural frequency of the displaceable portion112 to some degree. The natural frequency of the displaceable portion112 is determined by an elastic force of the connection portion 113, themass of the weight portion 132, and the like. When the cycle ofvibration applied to the displaceable portion 112 does not correspond tothe natural frequency, energy of the vibration applied to thedisplaceable portion 112 is dispersed, and the energy efficiencydecreases.

In addition, alternating voltage with a ½ frequency of the naturalfrequency of the displaceable portion 212 may be applied only to eitherbetween the driving electrodes 144 a, E1 or between the drivingelectrodes 154 a, E1.

(2) Generation of Force Caused by Acceleration

When the acceleration α is applied to the weight portion 132(displaceable portion 112), the force F0 acts on the weight portion 132.Specifically, according to the accelerations αx, αy, αz in the X, Y,Z-axis directions respectively, the forces F0 x (=m·αx), F0 y (=m·αy),F0 z (=m·αz) in the X, Y, Z-axis directions act on the weight portion132 (m is the mass of the weight portion 132). As a result, slants inthe X, Y directions and displacement in the Z direction occur in thedisplaceable portion 112. Thus, the accelerations αx, αy, αz cause theslants (displacements) in the displaceable portion 112 in the X, Y, Zdirections.

(3) Generation of Coriolis Force Caused by Angular Velocity

When the weight portion 132 (displaceable portion 112) moves in theZ-axis direction at a velocity vz, application of the angular velocity ωcauses a Coriolis force F to act on the weight portion 132.Specifically, according to the angular velocity ωx in the X-axisdirection and the angular velocity ωy in the Y-axis directionrespectively, Coriolis force Fy in the Y-axis direction (=2·m·vz·ωx) andCoriolis force Fx (=2m·vz·ωy) in the X-axis direction act on the weightportion 132 (m is the mass of the weight portion 132).

When the Coriolis force Fy caused by the angular velocity ωx in theX-axis direction is applied, a slant in the Y direction occurs in thedisplaceable portion 112. Thus, slants (displacements) in the Ydirection and X direction are generated in the displaceable portion 112by Coriolis forces Fy, Fx caused by the angular velocities ωx, ωy.

(4) Detection of Displacement of the Displaceable Portion 112

As described above, a displacement (slant) of the displaceable portion112 is caused by the acceleration α and the angular velocity ω. Thedisplacement of the displaceable portion 112 can be detected by thedetection electrodes 144 b to 144 e, 154 b to 154 e.

When the force F0 z in the Z positive direction is applied to thedisplaceable portion 112, distances between the detection electrodes E1(the upper face of the displaceable portion 112 c), 144 c and betweenthe detection electrodes E1 (the upper face of the displaceable portion112 e), 144 e both become small. Consequently, capacitances between thedetection electrodes E1 (the upper face of the displaceable portion 112c), 144 c and between the detection electrodes E1 (the upper face of thedisplaceable portion 112 e), 144 e both become large. That is, based onthe sum of capacitances between the detection electrodes E1 and thedetection electrodes 144 b to 144 e (or the sum of capacitances betweenthe detection electrodes E1 and the detection electrodes 154 b to 154e), the displacement in the Z direction of the displaceable portion 112can be detected and extracted as a detection signal.

On the other hand, when the force F0 y or the Coriolis force Fy in the Ypositive direction is applied to the displaceable portion 112, distancesbetween the driving electrodes E1 (the upper face of the displaceableportion 112 c), 144 c and between the detection electrodes E1 (the lowerface of the weight portion 132 e), 154 e become small, and distancesbetween the detection electrodes E1 (the upper face of the displaceableportion 112 e), 144 e and the detection electrodes E1 (the lower face ofthe weight portion 132 c), 154 c become large. Consequently,capacitances between the detection electrodes E1 (the upper face of thedisplaceable portion 112 c), 144 c and between the detection electrodesE1 (the lower face of the weight portion 132 e), 154 e become large, andcapacitances between the detection electrodes E1 (the upper face of thedisplaceable portion 112 e), 144 e and the detection electrodes E1 (thelower face of the weight portion 132 c), 154 c become small. That is,based on differences in capacitance between the detection electrodes E1and the detection electrodes 144 b to 144 e, 154 b to 154 e, a change inslant in the X, Y directions of the displaceable portion 112 can bedetected and extracted as a detection signal.

As described above, a slant in the X direction and the Y direction and adisplacement in the Z direction of the displaceable portion 112 aredetected by the detection electrodes E1, 144 b to 144 e, 154 b to 154 e.

(5) Extraction of Acceleration and Angular Velocity from DetectionSignals

Signals outputted from the detection electrodes 144 b to 144 e, 154 b to154 e, E1 include components caused by both the accelerations αx, αy, αzand the angular velocities ωx, ωy. Using a difference between thesecomponents, the acceleration and the angular velocity can be extracted.

A force Fα (=m·α) of when an acceleration α is applied to the weightportion 132 (mass m) does not depend on vibration of the weight portion132. Specifically, an acceleration component in a detection signal is akind of bias component that does not correspond to vibration of theweight portion 132. On the other hand, a force Fω (=2·m·vz·ω) of whenthe angular velocity ω is applied to the weight portion 132 (mass m)depends on the velocity vz in the Z-axis direction of the weight portion132. That is, an angular velocity component in a detection signal is akind of amplitude component that cyclically changes corresponding tovibration of the weight portion 132.

Specifically, the bias component (acceleration) with a frequency lowerthan a vibration frequency of the displaceable portion 112 and avibration component (angular velocity) similar to the vibrationfrequency of the displaceable portion 112 are extracted by frequencyanalysis of the detection signal. Consequently, it becomes possible tomeasure the accelerations αx, αy, αz in the X, Y, Z directions (threeaxes) and the angular velocities ωx, ωy in the X, Y directions (twoaxes) by the mechanical quantity sensor 100.

(Making of Mechanical Quantity Sensor 100)

Steps of making the mechanical quantity sensor 100 will be described.

FIG. 13 is a flowchart showing an example of a making procedure of themechanical quantity sensor 100. Further, FIG. 14A to FIG. 14K arecross-sectional views showing states of the mechanical quantity sensor100 (corresponding to a cross section of the mechanical quantity sensor100 taken along a line C-C in FIG. 1) during the making procedure inFIG. 13. FIG. 14A to FIG. 14K correspond to upside-down arrangements ofthe mechanical quantity sensor 100 of FIG. 11.

(1) Preparation of Semiconductor Substrate W (Step S10, and FIG. 14A)

As shown in FIG. 14A, there is prepared a semiconductor substrate Wformed by stacking three layers, first, second, and third layers 11, 12,13.

The first, second, and third layers 11, 12, 13 are layers for formingthe first structure 110, the joining part 120, the second structure 130respectively, and here they are formed of silicon containing impurities,a silicon oxide, and silicon containing impurities.

The semiconductor substrate W having a stack structure of the threelayers of silicon containing impurities/silicon oxide/silicon containingimpurities can be made by joining a substrate obtained by stacking asilicon oxide film on a silicon substrate containing impurities and asilicon substrate containing impurities, and thereafter polishing thelatter silicon substrate containing impurities to make it thin (what iscalled an SOI substrate).

Here, the silicon substrate containing impurities can be manufacturedby, for example, doping boron during manufacturing of a silicon singlecrystal by a Czochralski method.

An example of the impurities contained in the silicon is boron. As thesilicon containing boron, for example, one containing high-concentrationboron and having resistivity of 0.001 Ω·cm to 0.01 Ω·cm can be used.

Note that here the first layer 11 and the third layer 13 are formed ofthe same material (silicon containing impurities), but the first,second, and third layers 11, 12, 13 may all be formed of differentmaterials.

(2) Making of First Structure 110 (Etching of First Layer 11, Step S11,and FIG. 14B)

The first layer 11 is etched to form an opening 115, and form the firststructure 110. That is, using an etching method which can erode thefirst layer 11 but does not erode the second layer 12, predeterminedareas (openings 115 a to 115 d) of the first layer 11 is etched in athickness direction until an upper face of the second layer 12 isexposed.

A resist layer having a pattern corresponding to the first structure 110is formed on an upper face of the first layer 11, and exposed portionsnot covered by this resist layer are eroded downward vertically. In thisetching step, the second layer 12 is not eroded, and only thepredetermined areas (openings 115 a to 115 d) of the first layer 11 areremoved.

FIG. 14B shows a state that the first layer 11 is etched as describedabove to form the first structure 110.

(3) Making of Joining Part 120 (Etching of Second Layer 12, Step S12,and FIG. 14C)

The second layer 12 is etched to thereby form the joining part 120.Specifically, the second layer 12 is etched from its exposed portions inthe thickness direction and a layer direction, by an etching methodwhich can erode the second layer 12 but does not erode the first layer11 and the third layer 13.

In this etching step, it is unnecessary to form a resist layerseparately. That is, the first structure 110 being a residue portion ofthe first layer 11 functions as a resist layer for the second layer 12.The etching is performed on an exposed portion of the second layer 12.

In the etching step (Step S12) on the second layer 12, it is necessaryto perform an etching method that satisfies the following twoconditions. The first condition is to have directions in the thicknessdirection as well as the layer direction. The second condition is thatit can erode a silicon oxide layer but cannot erode a silicon layer.

The first condition is a condition necessary for not allowing thesilicon oxide layer to remain on an unnecessary portion and inhibitfreedom of displacement of the weight portion 132. The second conditionis a condition necessary for not allowing the erosion to reach the firststructure 110, on which processing to make a predetermined shape isalready completed, and the third layer 13, which are formed of silicon.

As an etching method that satisfies the first and second conditions,there is wet etching using buffered hydrofluoric acid (for example, amixed aqueous solution of HF=5.5 wt %, NH₄F=20 wt %) as an etchingsolution. Further, dry etching by an RIE method using a mixed gas of CF₄gas and O₂ gas is also applicable.

(4) Formation of Conduction Portions 160 to 162 (Step S13, and FIG. 14D)

The conduction portions 160 to 162 are formed as a, b below.

a. Formation of Conical Through Holes

Predetermined positions of the first structure 110 and the second layer12 are wet etched, and weight-shaped through holes penetrating up to thesecond layer 12 are formed. As the etching solution, a 20% TMAH(tetramethylammonium hydroxide) can be used for example to etch thefirst structure 110, and buffered hydrofluoric acid (for example, amixed aqueous solution of HF=5.5 wt %, NH₄F=20 wt %) can be used forexample to etch the second layer 12.

b. Formation of Metal Layers

On the upper face of the first structure 110 and in the conical throughholes, Al for example is deposited by a vapor deposition method, asputtering method, or the like, so as to form the conduction portions160 to 162. Unnecessary metal layers (metal layers outside edges (notshown) of upper ends of the conduction portions 160 to 162) deposited onthe upper face of the first structure 110 are removed by etching.

(5) Joining of First Base 140 (Step S14 and FIG. 14E)

1) Making of First Base 140

A substrate formed of an insulating material, for example, a glasssubstrate is etched to form the recessed portion 143, and then thedriving electrode 144 a, the detection electrodes 144 b to 144 e, andthe wiring layers L1, L4 to L7 are formed at predetermined positions bya pattern formed of Al containing Nd for example.

2) Joining of Semiconductor Substrate W and First Base 140

The semiconductor substrate W and the first base 140 are joined byanodic bonding for example.

The first base 140 is anodically bonded before making the secondstructure 130. Since the first base 140 is anodically bonded beforeforming the weight portion 132, no thin area exists in the connectionportions 113 a to 113 d, and thus they do not have flexibility. Thus,the displaceable portion 112 is not attracted to the first base 140 whenelectrostatic attraction occurs. Accordingly, joining of the first base140 and the displaceable portion 112 can be prevented.

FIG. 14E shows a state that the semiconductor substrate W and the firstbase 140 are joined.

(6) Second Structure 130 (Etching Third Layer 13, Step S15, and FIG. 14Fto FIG. 14H)

The second structure 130 is made as a to c below.

a. Formation of Gap 10 (FIG. 14F)

On the upper face of the third layer 13 excluding the formation area forthe weight portion 132 and its vicinity, a resist layer is formed, andan exposed portion (formation area for the weight portion 132 and itsvicinity) not covered by this resist layer is eroded downwardvertically. As a result, the gap 10 for allowing the weight portion 132to be displaced is formed above the area where the weight portion 132 isto be formed.

b. Formation of Recessed Portions 170 (FIG. 14G)

After the gap 10 is formed, recessed portions 170 are formed atpredetermined positions on an upper face of the area where the weightportion 132 is to be formed.

A resist layer is formed on an upper face of the area where the weightportion 132 is to be formed, and the resist layer in the areacorresponding to the recessed portions 170 is removed, thereby exposingthe third layer 13 in this area. Further, this exposed portion is erodedto form the recessed portions 170.

Conventionally, when the second base 150 and the second structure 130are anodically bonded (when the second glass substrate is anodicallybonded), it is possible that the weight portion 132 is attracted andjoined to the second base 150 by electrostatic attraction and adheringthereto, and the weight portion 132 does not operate, resulting in astate of not functioning as the mechanical quantity sensor 100.

Providing the recessed portions 170 allows to reduce electrostaticattraction between the weight portion 132 and the second base 150 whenthe second base 150 and the second structure 130 are anodically bonded,and adhesion of the weight portion 132 to the second base 150 issuppressed. Note that details of this will be described later.

c. Formation of Second Structure 130 (FIG. 14H)

The third layer 13 is etched to form the opening 133, the block lowerlayer portions 134 a to 134 j, and the pocket 135, thereby forming thesecond structure 130. Specifically, a predetermined area (opening 133)of the third layer 13 is etched in the thickness direction by an etchingmethod that erodes the third layer 13 and does not erode the secondlayer 12.

A resist layer having a pattern corresponding to the second structure130 is formed on the upper face of the third layer 13, and an exposedportion not covered by this resist layer is eroded downward vertically.

FIG. 14H shows a state that the second structure 130 is formed byetching the third layer 13 as described above.

In the above manufacturing process, it is necessary to perform anetching method as follows in the step of forming the first structure 110(Step S11), and the step of forming the second structure 130 (Step S15).

A first condition is to have directions in the thickness direction ofeach layer. A second condition is that it erodes a silicon layer butdoes not erode a silicon oxide layer.

An etching method satisfying the first condition is ICP etching method(Inductively-Coupled Plasma Etching Method). This etching method iseffective for opening a deep trench in a vertical direction, and is akind of etching method that is generally called DRIE (Deep Reactive IonEtching).

In this method, an etching stage of digging while eroding a materiallayer in a thickness direction and a deposition stage of forming apolymer wall on a side face of the dug hole are repeated alternately.The side face of the dug hole is protected by a polymer wall that isformed sequentially, and thus it becomes possible to allow the erosionto proceed almost only in the thickness direction.

On the other hand, to perform etching satisfying the second condition,an etching material having etching selectivity between a silicon oxideand silicon may be used. For example, it is conceivable to use a mixedgas of SF₆ gas and O₂ gas in the etching stage, and use a C₄F₈ gas inthe deposition stage.

(7) Joining of Second Base 150 (Step S16, and FIG. 14I)

1) Formation of Second Base 150

In a substrate formed of an insulating material, the driving electrode154 a, the detection electrodes 154 b to 154 e, and the wiring layersL2, L8 to L11 are formed at predetermined positions with a patternformed of Al containing Nd for example. Further, the second base 150 isetched to form 11 truncated conical through holes 10 for forming thewiring terminals T1 to T11 at predetermined positions.

2) Joining of Semiconductor Substrate W and Second Base 150

A getter material (made by, for example, SAES Getters Japan, productname: Non-evaporable Getter St122) is put in the pocket 135, and thesecond base 150 and the semiconductor substrate W are joined by anodicbonding for example.

On the rear face of the weight portion 132, the recessed portions 170are provided. Accordingly, as described above, electrostatic attractionbetween the weight portion 132 and the second base 150 is reduced whenthe second base 150 and the second structure 130 are anodically bonded,and adhesion of the weight portion 132 to the second base 150 isprevented. Note that details of this will be described later.

FIG. 14I shows a state that the semiconductor substrate W and the secondbase 150 are joined.

(8) Formation of the Wiring Terminals T1 to T11 (Step S17 and FIG. 14J)

Metal layers, for example, a Cr layer and an Au layer are formed in thisorder by a vapor deposition method, a sputtering method, or the like onthe upper face of the second base 150 and in the conical through holes10. Unnecessary metal layers (metal layers outside edges of upper endsof the wiring terminals T) are removed by etching, thereby forming thewiring terminals T1 to T11.

(9) Dicing of Semiconductor Substrate W, First Base 140, and Second Base150 (Step S18 and FIG. 14K)

The getter material in the pocket 135 is activated by, for example, heattreatment at 400° C., and thereafter the semiconductor substrate W, thefirst base 140, and the second base 150 joined together are cut by adicing saw or the like, to thereby separate them into individualmechanical quantity sensors 100.

Here, the principle of reduction of electrostatic attraction between theweight portion 132 and the second base 150 by the recessed portions 170and functioning of the recessed portions 170 as the adhesion preventingparts will be described.

FIG. 15 is a view showing a state that the weight portion 132 and thesecond base 150 face each other when the second base 150 and the secondstructure 130 are anodically bonded.

Since the gap 10 is formed above the weight portion 132, the second base150 and the weight portion 132 are arranged having the gap 10. Further,the second base 150 and a bottom face of a recessed portion 170 arearranged having a gap 10 a. A thickness d of the gap 10 a is larger thana thickness d0 of the gap 10 by a depth d1 of the recessed portion 170(d=d0+d1). As a result of movement of cations from the second base 150due to the anodic bonding, a negative space-charge layer 180 is formedin the vicinity (including the bottom portion of the recessed portion170) of the surface on the side close to the weight portion 132 of thesecond base 150. The gap 10 a between the bottom portion of the recessedportion 170 and the weight portion 132 can be assumed as a capacitor C1,the space-charge layer 180 as a capacitor C2, and the second base 150 asa resistor R, and thus the structure in FIG. 15 can be represented by anequivalent circuit shown in FIG. 16 in which the resistor R and the twocapacitors C1, C2 are connected in series.

At the moment that voltage is applied (t=0), the voltage to be appliedto the capacitors C1, C2 is zero since no charge is accumulated, andthus the entire voltage is applied to the resistor R.

After a sufficiently long time has elapsed (t=∞), the current becomeszero, and the voltage is applied to the two capacitors C1, C2. Inpractice, the voltage to be applied to the space-charge layer 180 issufficiently small, and it can be approximated that the entire voltageis applied to the gap 10 a. After the sufficiently long time haselapsed, energy φ accumulated in the gap 10 a can be expressed by thefollowing equation (1).

φ=(½)CV ₀ ²  equation (1)

Here, C=ε_(r)ε₀(S/d) is the capacitance of a capacitor, V₀ is appliedvoltage, ε_(r) is a relative dielectric constant, ε₀ is a dielectricconstant in vacuum, S is a cross-sectional area of the recessed portion170, d is the thickness of the gap 10 a.

Attraction F between electrodes of the capacitor C1 is expressed by thefollowing equation (2).

F=−(dφ/dx)_(x=d)=ε_(r)ε₀ V ₀ ²/2d ²  equation (2)

Therefore, when the second base 150 is anodically bonded, theelectrostatic attraction working on the weight portion 132 and thesecond base 150 is in inverse proportion to the square of the thicknessd of the gap 10 a. Accordingly, the distance between the weight portion132 and the second base 150 (thickness d of the gap 10 a) can be madelarge in the area where the recessed portion 170 is provided to therebyreduce the electrostatic attraction. In this manner, the recessedportion 170 functions as an adhesion preventing part that suppressesadhesion of the weight portion 132 to the second base 150 during anodicbonding.

Second Embodiment

FIG. 17 is an exploded perspective view showing a state that amechanical quantity sensor 200 according to a second embodiment of thepresent invention is disassembled. FIG. 18 is a cross-sectional viewtaken along a line D-D in FIG. 17. Parts common to FIG. 1 and FIG. 11are given the same reference numerals, and overlapping descriptions areomitted.

As shown in FIG. 17 and FIG. 18, the mechanical quantity sensor 200 ofthis embodiment is different from the mechanical quantity sensor 100 ofthe first embodiment in the following points.

First, in the mechanical quantity sensor 200 of this embodiment, wiringterminals T1 a to T11 a are formed in a first base 240 instead of thewiring terminals T1 to T11 formed in the second base 150 of themechanical quantity sensor 100 in the first embodiment.

Secondly, in the mechanical quantity sensor 200 of this embodiment, theconduction portions 262 are provided in the block upper layer portions114 c, 114 d, 114 g, 114 h, 114 j instead of the conduction portions 162formed in the block upper layer portions 114 a, 114 b, 114 e, 114 f, 114i of the mechanical quantity sensor 100 in the first embodiment.

The conduction portions 262 establish conduction between the block upperlayer portions 114 c, 114 d, 114 g, 114 h, 114 j and the block lowerlayer portions 134 c, 134 d, 134 g, 134 h, 134 j respectively, andpenetrate the block upper layer portions 114 c, 114 d, 114 g, 114 h, 114j and the joining part 123 respectively. The structures of theconduction portions 262 are the same as those of the conduction portions160 to 162 in the first embodiment.

The first base 240 is formed of, for example, a glass material, has asubstantially parallelepiped outer shape, and has a frame portion 241and a bottom plate portion 242. The frame portion 241 and the bottomplate portion 242 can be made by forming a recessed portion 243 in asubstantially rectangular parallelepiped shape (for example, 2.5 mmsquare and 5 μm deep) in a substrate.

In the first base 240, the wiring terminals Ta (T1 a to T11 a) areprovided penetrating the frame portion 241 and the bottom plate portion242, allowing electrical connections from the outside of the mechanicalquantity sensor 200 to the driving electrodes 144 a, 154 a and thedetection electrodes 144 b to 144 e, 154 b to 154 e. The structures ofthe wiring terminals T1 a to T11 a are the same as those of the wiringterminals T1 to T11 in the first embodiment.

A lower end of the wiring terminal T1 a is connected to an upper face ofthe projecting portion 111 b of the fixed portion 111. Lower ends of thewiring terminals T2 a to T9 a are connected to upper faces of the blockupper layer portions 114 a to 114 h, respectively (the numerical orderof T2 a to T9 a of the wiring terminals T2 a to T9 a corresponds to thealphabetical order of 114 a to 114 h of the block upper layer portions114 a to 114 h, respectively). The wiring terminals T10 a, T11 a areconnected to upper faces of the block upper layer portions 114 i, 114 j,respectively.

Therefore, similarly to the wiring terminals T2 to T11 in the firstembodiment, the wiring terminals T2 a to T11 a are connectedelectrically to the detection electrodes 144 e, 144 b, 154 b, 154 c, 144c, 144 d, 154 d, 154 e, and the driving electrodes 144 a, 154 a, inorder respectively.

Further, similarly to the wiring terminal T1 in the first embodiment,the wiring terminal T1 a is connected electrically to the electrodes E1formed in the upper face of the displaceable portion 112 and the lowerface of the weight portion 132.

As a result of movement of cations from the second base 250 due to theanodic bonding of the second base 250, a negative space-charge layer isformed in the vicinity of the surface on the side close to the weightportion 132 of the second base 250. In this embodiment, when the secondbase 250 is anodically bonded, the driving electrode 154 a and thedetection electrodes 154 b to 154 e are connected electrically toexternal grounds (grounded) via the wiring terminals T11 a, T4 a, T5 a,T8 a, T9 a connected electrically to the driving electrode 154 a and thedetection electrodes 154 b to 154 e, respectively. These groundeddriving electrode 154 a and detection electrodes 154 b to 154 e coverthe negative space-charge layer formed in the vicinity of the surface ofthe second base 250, and thus function as a shield layer which blocks anelectrostatic force. Accordingly, when the second base 250 is anodicallybonded, electrostatic attraction working on the lower face of the weightportion 132 and the upper face of the second base 250 can be reduced,and thus it is possible to suppress adherence of the weight portion 132to the second base 250.

Further, the recessed portions 170 are provided in the areascorresponding to areas on the rear face of the weight portion 132 wherethe driving electrode 154 a and the detection electrodes 154 b to 154 eare not arranged. Accordingly, as described above, it is possible tosuppress adherence of the weight portion 132 to the second base 150 whenthe second base 150 and the second structure 130 are anodically bonded.

As described above, with the mechanical quantity sensor 200 and themethod of manufacturing the same, the driving electrode 154 a and thedetection electrodes 154 b to 154 e can be made to function as a shieldlayer when the second base 250 is anodically bonded, and moreover, therecessed portions 170 provided on the rear face of the weight portion132 can be made to function as joining preventing parts. Accordingly,with the mechanical quantity sensor 200 and the method of manufacturingthe same, it is possible to more reliably suppress adhesion of theweight portion 132 to the second base 250 when the second base 250 isanodically bonded.

Further, in this embodiment, when the second base 250 is anodicallybonded, the driving electrode 144 a and the detection electrodes 144 bto 144 e are connected electrically to external grounds (grounded) viathe wiring terminals T10 a, T3 a, T6 a, T7 a, T2 a connectedelectrically to the driving electrode 144 a and the detection electrodes144 b to 144 e, respectively. Accordingly, even when a negativespace-charge layer is formed in the vicinity of the surface of the firstbase 240, the driving electrode 144 a and the detection electrodes 144 bto 144 e cover the surface of the first base 240, and thus function as ashield layer which blocks an electrostatic force. Accordingly, when thesecond base 250 is anodically bonded, electrostatic attraction workingon the upper face of the displaceable portion 112 and the lower face ofthe first base 240 can be reduced, and thus it is possible to furthersuppress adhesion of the displaceable portion 112 to the first base 240.

Moreover, in this embodiment, when the semiconductor substrate W and thesecond base 250 are anodically bonded, the wiring terminal T1 aelectrically connected to the weight portion 132 and the wiringterminals T2 a to T11 a electrically connected to the driving electrodes144 a, 154 a and the detection electrodes 144 b to 144 e, 154 b to 154 eare connected electrically on the outside via conducting wires or thelike.

Thus, when the second base 250 is anodically bonded, electricalconduction is established between the driving electrode 154 a and thedetection electrodes 154 b to 154 e arranged on the upper face of thesecond base 250 and the lower face of the weight portion 132, and theyhave equal potentials. No electrostatic attraction works between thedriving electrode 154 a and the detection electrodes 154 b to 154 e andthe lower face of the weight portion 132, which have equal potentials.Thus, in the mechanical quantity sensor 200 and the method ofmanufacturing the same, adhesion of the weight portion 132 to the secondbase 250 can further be suppressed when the second base 250 isanodically bonded.

Further, when the second base 250 is anodically bonded, the drivingelectrode 144 a and the detection electrodes 144 b to 144 e arranged onthe upper face of the first base 240 and the upper face of thedisplaceable portion 112 are electrically connected on the outside viaconducting wires or the like. Thus, electrical conduction is establishedbetween the driving electrode 144 a and the detection electrodes 144 bto 144 e and the upper face of the displaceable portion 112, and thusthey have equal potentials. No electrostatic attraction works betweenthe driving electrode 144 a and the detection electrodes 144 b to 144 eand the upper face of the displaceable portion 112, which have equalpotentials. Thus, in the mechanical quantity sensor 200 and the methodof manufacturing the same, adhesion of the displaceable portion 112 tothe first base 240 can further be suppressed when the second base 250 isanodically bonded.

Steps of making the mechanical quantity sensor 200 will be described.

FIG. 19 is a flowchart showing an example of a making procedure of themechanical quantity sensor 200.

The method of making the mechanical quantity sensor 200 of thisembodiment is different from the method of making the mechanicalquantity sensor 100 of the first embodiment in the following points.

First, in this embodiment, the wiring terminals T1 a to T11 a are formedin the second base 240 in step 25, instead of forming the wiringterminals T1 to T11 on the second base 150 in step 17 in the method ofmaking the mechanical quantity sensor 100 in the first embodiment.

Secondly, in this embodiment, in bonding of the second base 250 in step47, the wiring terminals T2 a to T11 a electrically connected to thedriving electrodes 144 a, 154 a and the detection electrodes 144 b to144 e, 154 b to 154 e are connected electrically to external grounds(grounded).

Thirdly, in this embodiment, in bonding of the second base 250 in step47, the wiring terminal T1 a connected electrically to the weightportion 132 and the wiring terminals T2 a to T11 a connectedelectrically to the driving electrodes 144 a, 154 a and the detectionelectrodes 144 b to 144 e, 154 b to 154 e are electrically connected onthe outside via conducting wires or the like.

Thirdly, in step 28, the conducting wires for example which connect thewiring terminal T1 a and the wiring terminals T2 a to T11 a on theoutside of the mechanical quantity sensor 200 are removed.

Third Embodiment

A mechanical quantity sensor 300 according to a third embodiment will bedescribed.

FIG. 20 and FIG. 21 are a bottom view of a second structure 330 formingthe mechanical quantity sensor 300 and a top view of a second base 150,respectively, and correspond to FIG. 6 and FIG. 8. FIG. 22 and FIG. 23are cross-sectional views showing states that the mechanical quantitysensor 300 is cut, and correspond to FIG. 10 and FIG. 11. Parts commonto the mechanical quantity sensor 100 of the first embodiment aredesignated the same numerals, and overlapping descriptions are omitted.

In the mechanical quantity sensor 300, unlike the mechanical quantitysensor 100, the recessed portions 170 are not arranged on the weightportion 132, and recessed portions 370 are arranged on the second base150. The recessed portions 370 are arranged between electrodes 154 (adriving electrode 154 a and detection electrodes 154 b to 154 e) on theupper face of the second base 350.

Similarly to the recessed portions 170 in the first embodiment, therecessed portions 370 on the second base 350 function as adhesionpreventing parts to reduce electrostatic attraction between the weightportion 132 and the second base 350 during joining. However, there aredifferences in advantages depending on differences in arrangement of therecessed portions 170, 370 (whether they are arranged on the weightportion 132 side or on the second base 350 side).

(1) When the Recessed Portions 370 are Arranged on the Base 350 Side

With this arrangement, there are advantages as follows.

Insulation performance becomes high between the electrodes 154.Arranging the recessed portions 370 between the electrodes 154 makes theelectrodes 154 tend to separate from each other. As a result,reliability of driving and detection with the electrodes 154 improves(it is difficult for noise to be mixed into signals).

There are small effect on the electrostatic capacitance between theelectrodes 154 (the driving electrode 154 a and the detection electrodes154 b to 154 e) and the electrodes E1 (see FIG. 12) on the lower face ofthe weight portion 132. That is, there is a small difference inelectrostatic capacitance between when the recessed portions 170, 370are not present and when they are present. The base 350 itself isinsulative, so the presence of the recessed portions 370 barely affectthe electrostatic capacitance as long as the electrodes 154 do notoverlap with the recessed portions 370. On the other hand, the weightportion 132 itself has conductivity (the entire bottom face of theweight portion 132 functions as the electrodes E1 due to doping or thelike of impurities into the semiconductor). Accordingly, when therecessed portions are formed on the weight portion 132 side, theelectrostatic capacitance changes irrespective of the location thereof.

(2) When the Recessed Portions 170 are Arranged on the Weight Portion132 Side

When the recessed portions 170 are arranged on the weight portion 132side, it is easy to make the bottom faces of the recessed portions 170larger than the gaps between the electrodes 154. Consequently, electricflux lines expand in the recessed portions 170 (particularly, in thevicinities of sides of the bottom portions of the recessed portions170), and electrostatic attraction between the weight portion 132 andthe second base 350 during joining is reduced (the density of theelectric flux lines decreases, and the electric field weakens).

When the bottom faces of the recessed portions 170 have almost the samesizes (areas) as the gaps between the electrodes 154, it is possiblethat the electrostatic attraction between the weight portion 132 and thesecond base 350 becomes large conversely. The electric flux lines aregenerated not only from the bottom faces of the recessed portions 170but from the side faces thereof. When the bottom faces of the recessedportions 170 have almost the same sizes as the gaps between theelectrodes 154, the side faces of the recessed portions 170 are atsmaller distances from the base 350 than the bottom faces. Accordingly,the electrostatic attraction between the side faces and the base 350becomes large (as shown in the above-described equation (2),electrostatic attraction is in inverse proportion to the distance).

(Method of Manufacturing the Mechanical Quantity Sensor 300)

The mechanical quantity sensor 300 can be made by a procedure similar tothat for the mechanical quantity sensor 100.

However, the method of making the mechanical quantity sensor 300 differsfrom the method of making the mechanical quantity sensor 100 in thefollowing points.

(1) Since the second structure 330 has no recessed portion, the step offorming recessed portions in the second structure 330 is not necessary(see S15 of the steps in FIG. 13).

(2) There is a step of forming the recessed portions 370 in the secondbase 350.

By etching a substrate formed of an insulating material, the recessedportions 370 and so on are formed, thereby making the second base 350. Aresist having openings corresponding to the recessed portions 370 and soon are formed on the substrate. For example, the recessed portions 370can be formed in the openings by wet etching using buffered hydrofluoricacid (BHF) or by dry etching using RIE.

Thereafter, the driving electrode 154 a, the detection electrodes 154 bto 154 e, and the wiring layers L2, L8 to L11 are formed on this secondbase 350 by a pattern formed of Al containing Nd for example.

Except the above points, the method of manufacturing the mechanicalquantity sensor 300 is not substantially different from the firstembodiment, and thus detailed descriptions thereof are omitted.

Other Embodiments

Embodiments of the present invention are not limited to theabove-described embodiments and can be extended and modified. Extendedand modified embodiments are included in the technical scope of thepresent invention.

For example, the mechanical quantity sensors 100 to 300 are describedwith examples of using a conductive material (silicon containingimpurities) for the first structure 110 and the second structure 130,but it is not always necessary that the entire body is formed of theconductive material. It may be arranged that at least necessary parts,such as the driving electrodes E1, the detection electrodes E1, partsestablishing conduction between the wiring terminal T10 and the upperface of the block upper layer portion 114 i, and the like, are formed ofthe conductive material.

1. A mechanical quantity sensor, comprising: a first structure having afixed portion with an opening, a displaceable portion arranged in theopening and displaceable relative to the fixed portion, and a connectionportion connecting the fixed portion and the displaceable portion, thefirst structure being formed of a first semiconductor material in aplate shape; a second structure having a weight portion joined to thedisplaceable portion and a pedestal arranged surrounding the weightportion and joined to the fixed portion, the second structure beingformed of a second semiconductor material and arranged and stacked onthe first structure; a first base connected to the fixed portion,arranged and stacked on the first structure, and formed of an insulatingmaterial; and a second base having a driving electrode applyingvibration in a stacking direction to the displaceable portion, arrangedon a face facing the weight portion, and formed of a conductivematerial, and a detection electrode detecting a displacement of thedisplaceable portion, arranged on a face facing the weight portion, andformed of a conductive material, the second base formed of an insulatingmaterial, connected to the pedestal, and arranged and stacked on thesecond structure, wherein the second structure has a recessed portionarranged in an area on a face of the weight portion facing the secondbase, the area corresponding to an area where the driving electrode andthe detection electrode are not arranged.
 2. A mechanical quantitysensor, comprising: a first structure having a fixed portion with anopening, a displaceable portion arranged in the opening and displaceablerelative to the fixed portion, and a connection portion connecting thefixed portion and the displaceable portion, the first structure beingformed of a first semiconductor material in a plate shape; a secondstructure having a weight portion joined to the displaceable portion anda pedestal arranged surrounding the weight portion and joined to thefixed portion, the second structure being formed of a secondsemiconductor material and arranged and stacked on the first structure;a first base connected to the fixed portion, arranged and stacked on thefirst structure, and formed of an insulating material; and a second basehaving a driving electrode applying vibration in a stacking direction tothe displaceable portion, arranged on a face facing the weight portion,and formed of a conductive material, and a detection electrode detectinga displacement of the displaceable portion, arranged on a face facingthe weight portion, and formed of a conductive material, the second baseformed of an insulating material, connected to the pedestal, andarranged and stacked on the second structure, wherein the second basehas a recessed portion arranged in an area which faces the weightportion and where the driving electrode and the detection electrode arenot arranged.
 3. A method of manufacturing a mechanical quantity sensor,comprising: forming a first structure having a fixed portion with anopening, a displaceable portion arranged in the opening and displaceablerelative to the fixed portion, and a connection portion connecting thefixed portion and the displaceable portion, by etching a first layer ofa semiconductor substrate formed by sequentially stacking the firstlayer formed of a first semiconductor material, a second layer formed ofan insulating material, and a third layer formed of a secondsemiconductor material; arranging and stacking a first base formed of aninsulating material on the first structure by joining the first base tothe fixed portion; by etching the third layer, forming a secondstructure having a weight portion joined to the displaceable portion, arecessed portion arranged on a face of the weight portion on a sideopposite to a face joined to the displaceable portion or on a face of anarea where the weight portion of the third layer is to be formed on aside opposite to a face joined to the displaceable portion, and apedestal arranged surrounding the weight portion and joined to the fixedportion; and arranging and stacking a second base on the secondstructure by anodically bonding the second base to the pedestal, thesecond base formed of an insulating material and having a first drivingelectrode arranged on a face facing the weight portion, formed of aconductive material, and applying vibration in a stacking direction tothe displaceable portion, and a first detection electrode arranged on aface facing the weight portion, formed of a conductive material, anddetecting a displacement of the displaceable portion, wherein therecessed portion is arranged in an area corresponding to an area wherethe first driving electrode and the first detection electrode are notarranged.
 4. A method of manufacturing a mechanical quantity sensor,comprising: forming a first structure having a fixed portion with anopening, a displaceable portion arranged in the opening and displaceablerelative to the fixed portion, and a connection portion connecting thefixed portion and the displaceable portion by etching a first layer of asemiconductor substrate formed by sequentially stacking the first layerformed of a first semiconductor material, a second layer formed of aninsulating material, and a third layer formed of a second semiconductormaterial; arranging and stacking a first base formed of an insulatingmaterial on the first structure by bonding the first base to the fixedportion; by etching the third layer, forming a second structure having aweight portion joined to the displaceable portion, a pedestal arrangedsurrounding the weight portion and joined to the fixed portion, and arecessed portion arranged in an area which faces the weight portion andwhere the first driving electrode and the first detection electrode arenot arranged; and arranging and stacking a second base on the secondstructure by anodically bonding the second base to the pedestal, thesecond base formed of an insulating material and having a first drivingelectrode arranged on a face facing the weight portion, formed of aconductive material, and applying vibration in a stacking direction tothe displaceable portion, and a first detection electrode arranged on aface facing the weight portion, formed of a conductive material, anddetecting a displacement of the displaceable portion.
 5. The method ofmanufacturing the mechanical quantity sensor according to claim 3,wherein the arranging and stacking the second base on the secondstructure is performed while the first driving electrode and the firstdetection electrode are grounded.
 6. The method of manufacturing themechanical quantity sensor according to claim 3, further comprising:forming a first conduction portion electrically connecting the fixedportion and the third layer between the forming the first structure andthe arranging and stacking the first base on the first structure; andforming a second conduction portion electrically connecting thedisplaceable portion and the third layer, wherein the arranging andstacking the second base on the second structure is performed whileconduction is established between the first driving electrode and thefirst detection electrode and the pedestal.
 7. The method ofmanufacturing the mechanical quantity sensor according to claim 3,wherein the first base has a second driving electrode applying vibrationin a stacking direction to the displaceable portion, arranged on a facefacing the displaceable portion, and formed of a conductive material,and a second detection electrode detecting a displacement of thedisplaceable portion, arranged on a face facing the displaceableportion, and formed of a conductive material; and wherein the arrangingand stacking the second base on the second structure is performed whilethe second driving electrode and the second detection electrode aregrounded.
 8. The method of manufacturing the mechanical quantity sensoraccording to claim 3, wherein the arranging and stacking the second baseon the second structure is performed while conduction is establishedbetween the second driving electrode and the second detection electrodeand the fixed portion.